The invention relates to a fibrous mat facer for preparing a gypsum board, to a gypsum board comprising said mat facer and to a system comprising said gypsum board. The fibrous mat comprises at least one ply of a non-woven fabric, and a binder composition, wherein the binder composition represents from 10 to 40 wt % of the total weight of the mat. The binder composition comprises a copolymer comprising a co-monomer unit of a vinyl ester of an alpha branched aliphatic monocarboxylic acid, said copolymer being present in an amount from 25 to 100 wt % of the binder composition weight.